This invention relates generally to the production of kinescopes and particularly to a gasket for sealing kinescope faceplates having out-of-flat sealing edges onto a vacuum chamber.
The production of color television picture tubes (kinescopes) is a very complex procedure employing literally hundreds of processing steps. Among the processing steps are those of producing a phosphor screen on the inside surface of a faceplate panel. The phosphor screen includes three different phosphors each of which produces one of the primary colors of light when impacted by electrons. The phosphor layer is coated with a layer of organic compound which provides a smooth surface so that a thin layer of aluminum can be applied to the screen. The aluminum coating is used to electrically connect the phosphor screen to a selection electrode (shadow mask) which causes each of three electron beams to impact the phosphor of the proper light emitting color. The aluminum layer also reflects light which is generated in the phosphor, but which is directed toward the interior of the tube, toward the viewer to enhance the brightness of the light from the screen.
The aluminum layer is applied to the screen of the panel by placing the panel over the open end of a vacuum chamber. The vacuum chamber is shaped and dimensioned in accordance with a particular model of faceplate panel. A support frame is arranged around the open end of the vacuum chamber to receive and support the panel. A resilient, non-porous gasket is arranged on the support frame to receive a seal edge of the panel. When the chamber is evacuated, atmospheric pressure pushes the seal edge of the panel onto a seal surface of the gasket to form an airtight seal between the gasket and the edge of the panel. As the edge of the panel presses into the gasket, the gasket deforms and the gasket material must be able to move, or creep, on the support frame to compensate for the dimensional change caused by the deformation. Typically, the need for the gasket to creep is no problem because the seal edge of the panel has very little curvature and, thus is sufficiently flat to require very little creep. Under these conditions, the seal edge is able to press against the seal surface of the gasket and form an airtight seal between the seal edge and the gasket. However, problems arise when the seal edges of the panels are curved, rather than straight, due to difficulty of forming glass, of which the panels are made. As the curvature of the seal edge increases, the depth to which the panel must push into the gasket material in order to form an air tight seal increases, the deformation of the gasket also increases. The increased deformation of the gasket material requires an increase in the ability of the gasket to creep, on-the support frame in order to form an air tight seal between the panel end gasket. With the prior art gasket, a panel edge curvature in the range of 10 mils, and above, prevents the formation of an air tight seal because of the limited amount of creep of the gasket. It is impossible to determine before hand whether or not a sufficiently airtight seal is formed prior to vaporizing the aluminum inside the vacuum chamber. The vaporization of the aluminum causes the aluminum to be deposited on the screen of the panel in the desired manner. However, when an effective airtight seal is not formed, some, or all, of the vaporized aluminum is oxidized and the aluminized coating on the phosphor screen is dark, and in many instances unacceptable. For these reasons there is a need for an improvement which permits an airtight seal to be formed between the gasket material and the seal edge of the panel even in the presence of substantial curvature of the seal edge. The present invention fulfills this need.